Interactions between penicillin and aqueous extracts of Plectranthus amboinicus and Plectranthus zeylanicus against Staphylococcus aureus.
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Date
2024
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Faculty of Science, University of Kelaniya Sri Lanka
Abstract
Penicillin, the pioneering antibiotic, has declined in effectiveness against Staphylococcus aureus due to increasing resistance, highlighting the urgent need for alternative strategies. Combining penicillin with medicinal plant extracts, such as Plectranthus amboinicus (Kapparawalliya) and Plectranthus zeylanicus (Iriveriya), rich in antibacterial compounds, offers a promising approach to revitalising its therapeutic efficacy. This study aimed to evaluate the potential interactions between penicillin and the aqueous extracts from P. amboinicus (PA) and P. zeylanicus (PZ) against both Methicillin-sensitive S. aureus (MSSA) and Methicillin-resistant S. aureus (MRSA). Whole plants of PA and PZ were macerated in distilled water for 24 hours at room temperature to prepare aqueous extracts. In the preliminary screening, the antibacterial activity of the aqueous extracts (500 mg/mL), and penicillin (3 mg/mL) were evaluated individually using the well-diffusion method. Ciprofloxacin (2 mg/mL) and distilled water were used as positive and negative controls, respectively. Subsequently, the minimum inhibitory concentration (MIC) of penicillin against MSSA and MRSA was determined using the broth microdilution method, followed by subculturing to determine minimum bactericidal concentrations (MBC). Aqueous extracts of PA and PZ were combined with different penicillin concentrations (2×MIC, MIC, 1/2×MIC, 1/4×MIC). The antibacterial activity of these combinations against MSSA and MRSA was evaluated using the well-diffusion method (well-diameter = 6 mm), measuring the inhibition zone diameter (IZD). The IZD of MIC of penicillin was compared with the IZD of penicillinPA and penicillin-PZ combinations to determine the interactions. Results showed that the aqueous extracts of PA and PZ did not demonstrate inhibition zones against MSSA and MRSA. The MIC and MBC of penicillin against MSSA were determined as 0.052 µg/mL and 100 µg/mL, respectively. However, the MIC of penicillin against MRSA was indeterminable, with an MBC exceeding 100 µg/mL. Notably, most combinations of penicillin with PA and PZ exhibited significantly higher IZD compared to MIC of penicillin alone (no inhibition zones), against both MSSA and MRSA (p < 0.05). Among all the combinations, the highest IZD was observed with the MIC+PZ combination against both MSSA and MRSA (IZD = 12.78 mm and 11.89 mm respectively). Potentiation was observed for the penicillin-PA combination, at penicillin concentration corresponding to the MIC against MSSA and at MIC, 1/2×MIC, 1/4×MIC against MRSA. With PZ, potentiation against MSSA and MRSA occurred at a penicillin concentration equivalent to the MIC. Additionally, penicillin combined with PZ demonstrated significantly stronger potentiation (p < 0.05) compared to penicillin-PA combinations, at equal penicillin concentrations, against both strains. In conclusion, the aqueous extracts from PA and PZ potentiated the antibacterial effectiveness of penicillin against MSSA and MRSA. This underscores the promise of these combinations for potent antibacterial therapies, suggesting a potential avenue for repurposing and reintroducing penicillin in combination with plant extracts to address antibiotic resistance. Further research should focus on understanding the mechanisms that enhance the effectiveness of penicillin when combined with PA and PZ.
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Keywords
Antibiotic resistance, Penicillin, Plectranthus amboinicus, Plectranthus zeylanicus
Citation
Hafsa M. F. F.; Darshana D.; Wickramasinghe S. S.; Tennakoon S. H.; Napagoda M. T. (2024), Interactions between penicillin and aqueous extracts of Plectranthus amboinicus and Plectranthus zeylanicus against Staphylococcus aureus, Proceedings of the International Conference on Applied and Pure Sciences (ICAPS 2024-Kelaniya) Volume 4, Faculty of Science, University of Kelaniya Sri Lanka. Page 60